Straw extrusion

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					?The pellets are transferred to another extrusion molder. The second straw extrusion is
fitted with a different type of die, which produces a hollow tube shape. The pellets are
dumped in a hopper on one end of the drinking straw machine and are forced through
a long channel by a screw mechanism. This screw is turned in the barrel with power
supplied by a motor operating through a gear reducer. As the screw rotates, it moves
the resin down the barrel. As the resin travels down the heated channel, it melts and
becomes more flowable. To ensure good movement and heat transfer, the screw fits
within the barrel with only few thousands of an inch clearance. It is machined from a
solid steel rod, and the surfaces almost touching the barrel are hardened to resist wear.
By the time the resin reaches the end of the barrel, it is completely melted and can be
easily forced out through the opening in the die.

The resin exits the die in a long string in the shape of a straw. It is then moved along
by a piece of equipment known as a puller which helps maintain the shape of the
straw as it is moved through the rest of the manufacturing process. In some processes,
it is necessary to pull the straw through special sizing plates to better control the
diameter. These plates are essentially metal sheets with holes drilled in them.
Eventually, this elongated tube is directed through a cooling stage—usually a water
bath. Some operations run the plastic over a chilled metal rod, called a mandrel,
which freezes the internal dimension of the straw to that of the rod. Ultimately, the
long tubes are cut to the proper length by a knife assembly.

				
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